Laminated Pane with Hologram Element

The invention relates to a laminated pane with a hologram element and a UV protection coating, to a method for producing such a laminated pane, and to the use thereof.

Laminated panes are nowadays used in many places, and in particular in vehicle construction. In this context, the term, “vehicle,” includes road vehicles, aircraft, ships, agricultural machinery, or even work equipment.

Laminated panes are also used in other areas. These include, for example, building glazing or information displays, e.g., in museums or as advertising displays.

Laminated panes are frequently also used as head-up displays (HUD) to display information. In this case, an image is projected onto the laminated glass panes by means of an imaging unit in order to display information in the viewer's field of view. In the vehicle sector, the imaging unit is arranged, for example, on the dashboard, such that the projected image is reflected in the direction of the viewer on the nearest glass surface of the laminated glass pane that is inclined towards the viewer (cf., for example, European patent EP 0 420 228 B1 or German patent application DE 10 2012 211 729 A1).

Head-up displays in which the projected image is reflected in the direction of the viewer on the nearest glass surface of the laminated glass pane that is inclined towards the viewer are subject to the law of reflection, according to which the angle of incidence and the angle of reflection are equal. The angle of inclination of the laminated glass pane cannot thus be freely selected.

Hologram elements laminated between the panes of a laminated pane can also be used for head-up displays. The hologram element has at least one hologram, and the hologram can contain information recorded therein. The hologram can be activated by means of light emitted by a projector and the information recorded in the hologram can thus be reproduced for the viewer. Head-up displays based on the principle of holography, so-called holographic head-up displays, are disclosed, for example, in publications WO 2012/156124 A1, US 2019/0056596 A1, U.S. Pat. Nos. 10,394,032 B2, 10,061,069 B2, and US 2015/205138 A1.

DE 10 2020 112 447 A1 discloses a method for integrating a hologram into a rigid component of a predetermined surface target geometry using a hologram-receiving layer of a liquid photopolymer.

A hologram can be produced in a holographic material, i.e., a photosensitive material, which is laminated between the panes of a laminated pane. To record a hologram, two, mutually-coherent light beams—the so-called reference beam—which can also be referred to as a reference wave, and the so-called object beam, which can also be referred to as an object wave, are directed onto a holographic material. The resulting interference pattern of the superimposed wave fronts is written to the holographic material as an alternating refractive index modulation. If the reference wave and the object wave have parallel wavefronts, the interference pattern corresponds to a parallel grating whose lamellae are angled below the angle bisector of reference wave and object wave. After recording, the holographic material is cured, thereby losing the ability to record further holograms. If the holographic material in which the hologram was recorded is again irradiated with the reference wave, the light at the recorded grating of the hologram is diffracted such that the diffracted wave corresponds to the object wave. By illuminating the interference pattern written into the holographic material with the reference wave, the object wave can thus be reconstructed.

Head-up displays in which the projected image is reproduced by means of a hologram in the direction of the viewer thus make it possible to produce laminated panes with laminated holograms, in which the angle of incidence on the laminated pane is not as large as the angle of reflection. Consequently, the angle of inclination of the laminated pane can be selected more freely for holographic head-up displays.

It is advantageous when producing a laminated pane with a hologram to record the hologram in the holographic material of a hologram element precursor only after the lamination process, since the lamination process can have a negative effect upon the optical properties of a recorded hologram. A method for producing a laminated holographic display in which the hologram is recorded only after lamination is disclosed, for example, in EP 3 461 636 B1.

However, recording a hologram in the holographic material of a hologram element precursor laminated between two glass panes is problematic, because any change in the refractive index causes reflections of the object beam and the reference beam when the hologram is being recorded. Thus, undesirable reflections on the surfaces of the two glass panes facing away from the holographic material lead to undesirable interference patterns, and thus to undesirable gratings recorded in the holographic material. These undesirable, recorded gratings result in the hologram showing undesirable artifacts when irradiated with the reference wave after the holographic material has cured. In addition, the undesirable gratings recorded in the hologram can be activated from the outside by external light sources. This leads to unnecessary distractions and possibly glare for the viewer, and should therefore be minimized for safety reasons.

In the context of the present application, the term, “hologram element precursor,” means the precursor of a hologram element. A hologram element precursor does not have a hologram. By recording at least one hologram by exposing the holographic material of a hologram element precursor to an object beam and a reference beam, a hologram element is obtained. The hologram element obtained differs from the hologram element precursor in that at least one hologram is recorded in the hologram element.

In WO 2021/087286 A1, a replication tool for use in producing a holographic film by replication is disclosed, and a method for producing laminated glazing using the replication tool is disclosed. During replication, an oil or gel having a matching refractive index may be arranged in a cavity between the laminated glazing and the main holographic film arrangement to reduce reflections during replication and improve the quality of the laminated glazing.

Whereas, in head-up displays in which the projected image is reproduced by means of a hologram in the direction of the viewer, a reflection of the reference wave on the outer surface of the outer pane is attenuated as a result of diffraction at the recorded grating of the hologram; in particular, a reflection of the reference wave on the interior surface of the inner pane can appear as a weak but nevertheless interfering ghost image. If the light emitted by a projector and incident upon the laminated pane at the Brewster (incidence) angle is exclusively p-polarized, the reflected portion of the light at the Brewster angle is close to zero.

Holographic materials for holographic HUD applications, for example for windshields in vehicles, can be photosensitive polymers (PP) or gels. Such photosensitive materials are commercially available. It is known that incident light, in particular in the ultraviolet spectrum, can significantly influence the physical properties of such photosensitive materials of holographic films over time. The typical service life and durability of windshields is approximately 7 to 12 years, in the area of trucks 2 to 4 years. The aging effects that are observed within such time periods relate, inter alia, to the change in color (discolorations), the mechanical and physical properties, the size and even the holographic properties of these films.

WO 2021/091818 A1 discloses a laminated glass pane which provides for an intermediate layer with UV-absorbing particles for protecting the holographic medium from UV light between the outer pane and the holographic medium. A second intermediate layer remains without UV-light-absorbing particles in order to enable the UV curing of the photosensitive polymer. After the completed curing and lamination to form the laminated pane, a UV-light-absorbing coating is applied to the inner side of the inner pane (side IV).

WO 2021/219285 A1 describes a vehicle pane comprising an electroluminescent device and an optical band-blocking filter, wherein the electroluminescent device emits light and the optical band-blocking filter significantly reduces the radiation of the electroluminescent device in one emission direction. In this way, the emission of light in an undesired emission direction is prevented. The band-blocking filter is designed as a thin-film coating comprising optically high-refractive layers having a refractive index greater than 1.8 and optically low-refractive layers having a refractive index of less than 1.8.

WO 2021/041635 A1 discloses a method for producing a glazing, wherein a first glass pane, a first intermediate layer, a photopolymer film, a second intermediate layer and a second glass pane are laminated together and the photopolymer film is subsequently exposed. Optionally, the glazing comprises an infrared-reflecting layer which, in turn, may optionally be at least partially reflective even within other wavelength ranges, such as in the ultraviolet range.

US 2022/0176682 A1 discloses an intermediate layer for laminated panes, which comprises a hologram element and a first thermoplastic intermediate layer, wherein the first thermoplastic intermediate layer contains a UV absorber.

The object of the present invention is to provide, in particular for a head-up display, an improved laminated pane with a hologram element, in which pane the hologram element in particular can have improved durability and service life. In particular, aging processes, such as the deterioration properties, in particular the holographic properties, or a color changes in the visible spectrum are to be avoided or at least significantly delayed. In addition, the laminated pane with the holographic HUD is to be simple and inexpensive to produce, even in industrial series production.

The object of the present invention is achieved by a laminated pane according to independent claim. Preferred embodiments are apparent from the dependent claims. A method for producing a laminated pane according to the invention and the use thereof are apparent from further independent claims.

The invention relates to a laminated pane at least comprising an outer pane having an outer surface and an interior surface, an inner pane having an outer surface and an interior surface, a first intermediate layer, and a hologram element having at least one hologram.

The first intermediate layer is arranged between the outer pane and the inner pane, and the hologram element is arranged between the outer pane and the first intermediate layer or between the inner pane and the first intermediate layer.

According to the invention, a UV protection layer is applied to the interior surface of the outer pane (side II) at least in the region of the hologram element. In the region of the hologram element, this means that a projection of the hologram element into the plane of the UV protection layer overlaps the latter in terms of area. In a view through the laminated pane, the UV protection layer thus lies between the outer pane and the hologram element so that the UV radiation impinging through the outer pane on the hologram element first passes through the UV protection layer. The UV protection layer is also referred to as UV protection coating, i.e., is applied in the form of a coating directly to the interior surface (side II) of the outer pane. The UV protection layer applied to the side II of the outer pane can thus advantageously prevent or at least largely avoid aging processes and changes in the material properties of the hologram element caused by UV radiation in sunlight from the outside, or can delay them beyond the typical lifetime of the laminated pane. In particular, changes in the photosensitive material by the incident sunlight, and in particular the UV light component, and associated change and deterioration of the holograms recorded in the holographic material can be effectively prevented or at least largely avoided. As a result, the durability of the laminated pane with a constant quality of the holographic HUD function can advantageously be significantly prolonged.

The outer pane, also referred to as the first pane, constitutes a pane of the laminated pane that is adjacent to the outside environment in the installed state of the laminated pane. The outer pane has an exterior surface, also referred to as side I, facing towards and adjacent to the vehicle surroundings. The pane surface of the outer pane opposite the outer surface of the outer pane is referred to as the interior surface, also called side II, of the outer pane and, in the installed state of the glazing, faces toward the interior. The inner pane, also referred to as the second pane, constitutes the pane of the laminated pane that faces the interior in the state installed in a vehicle. The inner pane has an outer surface, also referred to as side III, which faces toward the outer pane and the environment in the installed state. The pane surface of the inner pane opposite the outer surface of the inner pane is referred to as the interior surface of the inner pane, also called side IV, and adjoins the interior in the installed state.

The laminated pane is preferably a vehicle pane, i.e., it is suitable for installation in a vehicle, wherein the vehicle pane separates the vehicle interior from the vehicle environment in the installed state.

In one embodiment, the UV protection layer is formed from a UV-light-reflecting and/or UV-light-absorbing material.

In a preferred design, the UV protection layer comprises at least one layer of an optically high-refractive material, preferably having a refractive index of greater than or equal to 1.8, particularly preferably greater than or equal to 1.9, in particular greater than or equal to 2.

In a preferred embodiment, the UV protection layer is preferably an optically high-refractive layer, in particular having a refractive index greater than 1.8, which is designed as a coating, particularly preferably on the basis of silicon nitride, zinc tin oxide, silicon-zirconium nitride or titanium oxide (TiOx).

According to the invention, the optically high-refractive layer can be formed, for example, on the basis of titanium dioxide, silicon nitride, tin zinc oxide, silicon-zirconium nitride, silicon-titanium nitride, or silicon-hafnium nitride.

If a layer is formed on the basis of a material, the layer consists predominantly of this material, in particular substantially of this material, in addition to any impurities or doping. For example, the UV protection layer can be formed from the mentioned material to more than 95 wt. %, preferably more than 97 wt. %, for example 98 wt. % or more (of the UV protection layer).

These high-refractive layers can preferably be formed with a thickness of 10 nm to 100 nm, particularly preferably with a thickness of 20 nm to 50 nm.

In another design, the UV protection layer is multi-ply and comprises at least one layer of an optically high-refractive material and at least one layer of an optically low-refractive material.

In a further preferred embodiment, it is provided that the multi-ply UV protection layer comprises at least two layers (plies) of a high-refractive material, which are preferably separated from one another by a layer of optically low-refractive material.

According to the invention, the UV protection coating can be formed from alternately arranged layers with different refractive indices. The multi-ply UV protection coating preferably comprises at least two optically high-refractive layers, in particular having a refractive index greater than 1.8, and at least one optically low-refractive layer, in particular having a refractive index of less than 1.8, e.g., less than 1.6. Starting from the interior surface of the outer pane, first a first high-refractive layer, thereon a first low-refractive layer, thereon a second high-refractive layer are arranged on top of one another, preferably over the entire surface. Such an embodiment has proven to be particularly advantageous with regard to the UV protection effect of the coating. The high-refractive layers can be formed, for example, on the basis of silicon nitride, zinc tin oxide, silicon-zirconium nitride or titanium oxide; the low-refractive layers can be formed, for example, on the basis of silicon dioxide or magnesium fluoride. Both the materials of the optically high-refractive and also those of the low-refractive layers (plies) of the UV protection layer can be doped, for example with further transition metal oxides, such as ZnO, ZrO, HfOx.

In the context of the present invention, refractive indices are generally given relative to a wavelength of 550 nm. The refractive index can be determined, for example, by ellipsometry. Ellipsometers are commercially available-for example, from Sentech. The refractive index of a dielectric layer is preferably determined by first depositing it as a single layer on a substrate and subsequently measuring the refractive index by ellipsometry. Dielectric layers with the mentioned refractive indices and methods for their deposition are known to the person skilled in the art in the field of thin layers. Preferably, methods of physical vapor deposition, and in particular magnetron sputtering, or wet coating are used.

The optically low-refractive layers, for example made of silicon dioxide or magnesium fluoride, can preferably be formed with a thickness of 10 nm to 100 nm, particularly preferably with a thickness of 20 nm to 50 nm.

In an exemplary embodiment, the UV protection coating, starting from the interior surface of the outer pane, is formed as a three-ply UV protection layer from a 35 nm thick titanium dioxide layer, a 35 nm thick silicon dioxide layer arranged thereon, a 30 nm thick titanium dioxide layer arranged thereon.

In one embodiment of the invention, the single-ply or multi-ply UV protection layer is formed with a layer thickness of 10 nm to 200 nm, preferably of 20 nm to 100 nm, and particularly preferably of 30 nm to 80 nm.

In another design of the laminated pane according to the invention, the single-ply or multi-ply UV protection coating is formed from a UV-light-absorbing material or comprises such a material. Known examples suitable for the invention are organic layers, for example based on benzotriazole (e.g., commercially available under the trade name Tinuvin® from BASF), triazine or benzophenone or combinations thereof.

According to the invention, such organic UV protection layers are preferably formed with a thickness between 1 μm and 100 μm, for example with a thickness between 10 μm and 80 μm, for example with 20 μm, 40 μm, 50 μm or 60 μm.

The outer pane and the inner pane each have an exterior surface, i.e., an outer surface, and an interior surface, i.e., an inner surface, and a circumferential side edge extending therebetween. For the purposes of the invention, the term, “external surface,” refers to the main surface which, when installed, is intended to face the external surroundings. For the purposes of the invention, the term, “interior surface,” refers to the main surface which, when installed, is intended to face the interior. The interior surface of the outer pane and the exterior surface of the inner pane face one another in the laminated pane according to the invention.

The surfaces of the glass panes are typically referred to as follows:

The exterior surface of the outer pane is referred to as side I. The interior surface of the outer pane is referred to as side II. The exterior surface of the interior pane is referred to as side III. The interior surface of the inner pane is referred to as side IV.

If the laminated pane is provided in a window opening of a vehicle or of a building to separate an interior from the external environment, the term “inner pane,” for the purposes of the invention, refers to the pane facing the interior (vehicle interior). The outer pane refers to the pane facing the external surroundings.

The hologram element refers to the holographic medium in which the hologram is contained. The hologram element comprises a photosensitive material, i.e., a holographic material. A hologram can be recorded therein by exposure to a suitable light source. In the finished laminated pane, the material of the hologram element is no longer light-sensitive, because the holographic material is changed during the process to such an extent that no further recording of a hologram is possible.

The hologram element comprises a holographic material, and can additionally optionally comprise a first substrate layer and/or a second substrate layer. Suitable holographic materials are known to the person skilled in the art. Suitable first and second substrate layers are likewise known to the person skilled in the art.

Preferably, the hologram element comprises a photopolymer, dichromate gelatin, or silver halide gelatin, and particularly preferably a photopolymer, as the holographic material.

Silver halides or dichromates are typically used in a matrix of gelatin, which is first usually dried at room temperature before a hologram can be recorded by exposure to light.

In one embodiment, the holographic material is formed as a coating of the interior surface of the outer pane or as a coating of the outer surface of the inner pane.